A lot of confusion falls with many believing that all blue light is bad. This is not true. We all need blue light to view colors and for our personal circadian rhythm. Some use blue light tester pens but do not understand blue light. The blue light wavelength in the laser pens are 405nm; this does not apply properly to blue light lenses. When testing our lenses, the laser pen light will not pass thru the lens; yet some blue light will filter through- this is not harmful blue light. Our UV420 will block up to 420nm, rendering the tester pen with 405nm not compatible for testing. You end up missing the point of the tester pen.